The present invention generally pertains to communication signal processing and is particularly directed to the preparation and detection of preambles in direct sequence spread spectrum (DSSS) and narrow band signals.
The present invention provides a method of processing preambles of signals that are to be transmitted as direct sequence spread spectrum (DSSS) signals and narrowband signals to prepare the preambles for transmission, comprising the steps of:
(a) when the signal is to be transmitted as a narrow band signal, providing an unspread preamble that includes a sequence of blocks, with each of the blocks having the same number of code elements in the same predetermined pattern;
(b) when the signal is to be transmitted as a DSSS signal, providing a spread preamble that includes a sequence of the same number of blocks as the number of blocks in the unspread preamble, with each of the blocks of the spread preamble having a number of code elements corresponding to a spread-factor multiple of the number of code elements in each of the blocks of the unspread preamble, with each of the blocks of the spread preamble having the same predetermined pattern of code elements; wherein the spread factor is an integer greater than one;
(c) providing a preamble encoding sequence that includes the same given number of code elements as the number of blocks of the preamble; and
(d) using encoding means to encode the sequence of preamble blocks with sequentially corresponding code elements of the preamble encoding sequence to thereby provide a sequence of encoded preamble blocks.
The present invention also provides a method of detecting a preamble in a received signal, wherein the received signal includes a sequence of encoded preamble blocks, each of which blocks has the same number of code elements, wherein the sequence of encoded preamble blocks has been provided by encoding a sequence of identical preamble blocks with sequentially corresponding code elements of a preamble encoding sequence, and wherein each of the identical preamble blocks has the same predetermined pattern of code elements, the method comprising the steps of:
(a) using sampling means to periodically sample a received signal having said sequence of encoded preamble blocks to provide of a sequence of received signal samples;
(b) processing the received signal samples to provide a first metric representing an average energy of the received signal;
(c) processing the received signal samples with the predetermined pattern of code elements of the identical preamble blocks that were encoded to provide the sequence of encoded preamble blocks, to thereby provide samples of the received signal that are correlated with the predetermined pattern of code elements;
(d) processing the correlated samples to provide a second metric representing a noncoherent accumulation of energy over a first accumulation interval having a duration corresponding to the duration of a plurality of encoded preamble blocks;
(e) processing the correlated samples with the preamble encoding sequence, to thereby provide a third metric representing a coherent accumulation of energy over a second accumulation interval approximating the duration of the sequence of encoded preamble blocks; and
(f) processing the second metric with the first metric and the third metric to detect a preamble in the received signal.
This method can be used for detecting the predetermined preamble in both signals that are transmitted as narrow band signals and signals that are transmitted as DSSS signals, provided that the preambles for both types of signals are prepared for transmission in accordance with the method of the present invention.
The present invention thereby provides compatible preparation and detection of a preamble in narrow band and DSSS signals.
The present invention additionally provides a system for performing the above-described preamble detection method and computer readable storage media containing instructions for accomplishing various steps of such method.
Additional features of the present invention are described with reference to the detailed description of the preferred embodiments.